Where exactly is this crack? If it is after the MAF, this could be causing the problem. If it isn't, then I do not think it is.

If it is after the MAF, then you are having an unspecified amount of unmetered air enter the intake and it would be leaning your mix out, and over time your computer will try and compensate by messing with the fuel trims. I am surprised you haven't noticed it running poorly, since the timing would probably get pretty wacky too.

If the crack is before the MAF, then there is something else in play here.


Weren't you having some other issues as well a week or two ago?

Followup
 

Attached is a schematic of the intake system and circled in red is the problem part. Looks like a fairly easy fix (famous last words)

Thanks all!

Re: comments
 

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Yeah, the crack is just before where the MAF inserts in (I think)

The performance isn't great but the only noticeable difference is the level of torque in 1st and 2nd gear driving...

Still sorting through the clutch issue. I figure I will wait 10 minutes for something else to break and then try to get a large repair discount from a mechanic (j/k)

Thanks

If the crack is ahead of where the computer reads the amount of air entering the throttlebody, then this is not causing your issue.

I had this same issue. Low power,whistling, wankie shifting, rough idol ( wont idol in cold), jumping and bucking on take off. I nursed it through the winter but only made it worse! I found the repair part (Intake Elbow) on BMW Parts and BMW Accessories | Bavarian Autosport for $25 shipped. Took less than 15 min. to repair.

Surprised there isn't a check engine light for that cracked elbow. That should fix your gas mileage and running. Very easy fix.
The oil service lights are just there for informational purposes only. Will not affect anything other than your sanity.

Are you sure you aren't leaking fuel? For you to visually see the gas needle drop on short trips I'd guess something is leaking. Check the fuel line connections at the fuel filter as well as the lines all along the underside of the car.

Unfortunately what he has circle is the idle control valve connection to the throttle plate which is AFTER the MAF which is what measure the amount of air entering the engine.

You have unmetered air entering the engine which is causing a lean condition. To compensate for a LEAN mixture the DME is commanding the injectors to add additional fuel to the mixture.

If you don't have a SES you more then likely have a PENDing fault code.

Could also be a rusted fuel line. Several members have already reported on rusted fuel lines.

You may want to see if you're popping codes for the O2 sensors. If you are experiencing loss of power during any acceleration, check the disa valve. Good luck.